Bar codes have hitherto been widely used as a means to impart unique information to a medium such as plastics, paper or the like for its autorecognition. For example, one dimensional bar codes are widely used for general consumer goods for the purpose of the POS management system, inventory management or the like. Furthermore, as the applications of bar codes are expanded, the demands on the information volume of bar codes increase, and the symbol information referred to as two dimensional bar codes, which have a significantly greater capacity than one dimensional bar codes, are making their appearance. And readout devices to deal with the two dimensional codes are also gradually being used widely.
Among these two dimensional bar codes, one form is to increase the information volume by piling up the one dimensional codes; this is called stack-type bar codes. For a representative one, there is a code system stack-type bar code referred to as PDF 417. Moreover, this code system PDF 417 is an international standard.
For the readout device to read out stack-type bar codes, there is a readout device described in Japanese Kokai Patent Application No. H2-268383 or Japanese Kokai Patent Application No. H5-324887 (Paragraph [0013]). The bar code reader disclosed in Japanese Kokai Patent Application No. H2-268383 images bar codes with a two dimensional imaging device, integrates the image into memory, and decodes the bar code symbol information based on the above data.
However, the bar code reader disclosed in Japanese Kokai Patent Application No. H2-268383 has a problem that readout precision becomes dependent on the direction of the label of stack-type bar codes, and also a problem that it does not take into consideration a situation in which the label is imaged outside the view of the imaging device. The symbol information readout device disclosed in Japanese Kokai Patent Application No. H5-324887 (Paragraph [0013]) solves such problems. In the symbol information readout device disclosed in Japanese Kokai Patent Application No. H5-324887 (Paragraph [0013]), bar codes are imaged with the two dimensional imaging device, and the bar code position and inclination are detected. As a result, whatever direction the label of stack-type bar codes is set to, or even if the image has defects, the symbol information readout device is arranged so as to be able to read out the bar code symbol information.
Moreover, Japanese Kokai Patent H9-050480 discloses a symbol information readout device which used is a line sensor that reads out without correcting the inclination to rearrange a recording medium when the symbol of two dimensional bar codes is placed.